WO2008108501A1

WO2008108501A1 - ABNORMALITY DIAGNOSIS DEVICE FOR NOx SENSOR

Info

Publication number: WO2008108501A1
Application number: PCT/JP2008/054555
Authority: WO
Inventors: Hiroshi Sawada; Shinichiro Imamura
Original assignee: Toyota Jidosha Kabushiki Kaisha; Denso Corporation
Priority date: 2007-03-06
Filing date: 2008-03-06
Publication date: 2008-09-12
Also published as: EP2119897A1; US8091404B2; EP2119897A4; EP2119897B1; JP4537417B2; JP2008215260A; US20100024520A1; CN101646855A; CN101646855B

Abstract

An exhaust path of an internal combustion engine is provided with a NOx storage reduction catalyst and a post-catalyst NOx sensor for detecting the NOx concentration downstream of the NOx catalyst. The NOx concentration upstream of the NOx catalyst is detected or estimated. Under the condition that the NOx catalyst substantially does not store NOx contained in exhaust gas, the detected or estimated NOx concentration upstream of the NOx catalyst and the NOx concentration detected by the post-catalyst NOx sensor are compared with each other to determine abnormality of the post-catalyst NOx sensor. Abnormality diagnosis is performed with an influence of the NOx catalyst eliminated.

Description

Specification

NO x sensor abnormality diagnosis device Technical Field

The present invention relates to an abnormality diagnosis device for an NO X sensor, and more particularly, to an abnormality diagnosis device for an NOx sensor provided on the downstream side of the NOx storage reduction catalyst. Background art

In general, NO X catalysts for purifying NO X (nitrogen oxides) contained in exhaust gas are known as exhaust gas purification devices installed in exhaust systems of internal combustion engines such as diesel engines and lean burn gasoline engines. Yes. Various types of NO X catalysts are known. Among them, NOx storage reduction (NSR), which stores and removes NO X in exhaust gas, is known. It is known. The NOx storage reduction catalyst stores NO X in the exhaust gas when the air-fuel ratio of the supplied exhaust gas is leaner than the predetermined value (typically the stoichiometric air-fuel ratio) (ie, an oxygen-excess atmosphere) When the air-fuel ratio of the supplied exhaust gas is richer than the predetermined value (ie, oxygen-deficient atmosphere), the stored NO X is released and reduced to N ₂ . When the NOx storage reduction catalyst stores NO X in a saturated state, that is, full, the NO X catalyst can no longer store NO X. Therefore, at appropriate time intervals, a reducing agent is supplied to the Nx catalyst, the NOX catalyst is placed in an oxygen-deficient atmosphere, and the NOX storage capacity is released from the NOX catalyst to restore the NOX storage capacity of the NOX catalyst. Is done. This is called N0x regeneration.

For example, in order to determine the start and end timing of this NO X regeneration, a NOX sensor that detects the NOX concentration in the exhaust gas is provided downstream of the NO X catalyst. For example, when NO X is occluded until the NO X catalyst is full, NO X leaks to the downstream side of the catalyst, so NO X regeneration can be started when the NOX sensor detects this leaked NOX. Les. In addition, during NOx regeneration, when the NOx concentration detected by the NOx sensor has dropped sufficiently, it can be considered that all of the stored NOx has been released, so NOx regeneration can be terminated. By the way, in the case of an engine mounted on an automobile, for example, it is also possible to detect abnormalities in the catalyst or sensor in the on-board state (on-board) according to the laws and regulations of each country in order to prevent traveling in a state where exhaust gas has deteriorated. It has been requested. Relatively many technologies already exist for the detection of catalyst abnormalities. However, as described above, there is currently no effective technique for detecting abnormalities in the NOX sensor installed downstream of the NOx catalyst. In particular, as exhaust gas regulations are becoming stricter, it is required to detect not only failures such as disconnection, but also the accuracy of sensor output related to deterioration, and so on. Countermeasures are necessary.

As a method of diagnosing abnormalities in this NO X sensor, for example, multiple NO X sensors can be installed at the same position and their detected values can be compared relatively, or NO X sensors can be removed and checked with a fixed analyzer. A way to do this is conceivable. However, in the former case, the cost is high, and in the latter case, on-board diagnosis is impossible.

Japanese Patent Laid-Open No. 2003-1 20399 discloses an abnormality detection apparatus for a NOx sensor provided downstream of a NOx absorbent. When the NOx concentration of the exhaust gas that reaches the NO X sensor is forcibly changed and the fluctuation of the NOx sensor output value deviates from the fluctuation when the sensor is normal, the NOx sensor is judged to be abnormal.

However, since the exhaust gas that reaches the NOX sensor is exhaust gas after passing through the NOx absorbent, the NOx concentration of the exhaust gas is the same as the concentration after NOx is absorbed by the NOx absorbent. Become. In other words, the output value of the NO X sensor reflects the effect of the NO X absorbent in front of the sensor, which causes a decrease in the accuracy of NOX sensor abnormality diagnosis. Disclosure of the invention

The present invention has been made in view of the above circumstances, and an object of the present invention is to suitably detect an abnormality in a NOX sensor provided on the downstream side of the NOx storage reduction catalyst. The object is to provide an abnormality diagnosis device for a NO x sensor.

According to the first aspect of the present invention,

An NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;

A post-catalyst N O X sensor for detecting the N O X concentration of exhaust gas downstream of the N O X catalyst;

Pre-catalyst NO X concentration acquisition means for detecting or estimating the NOx concentration of exhaust gas upstream of the NOx catalyst;

The NOX concentration detected by the post-catalyst NOX sensor and the NOx concentration detected or estimated by the pre-catalyst NOX concentration acquisition means under the condition that the NO X catalyst does not substantially store NO X in the exhaust gas. And an abnormality determination means for determining abnormality of the post-catalyst NOX sensor

An NOx sensor abnormality diagnosis device characterized by comprising:

Under the condition that NO X catalyst does not substantially store NO X in the exhaust gas, NOx flowing into the NO X catalyst passes through the NOx catalyst and reaches downstream of the NOx catalyst. Therefore, the NOx concentration upstream of the NOx catalyst is almost equal to the NOx concentration downstream of the N0x catalyst. Therefore, if the NOx concentration detected by the post-catalyst NOx sensor deviates from the NOx concentration upstream of the NOx catalyst, the post-catalyst NOx sensor can be determined to be abnormal. Abnormality diagnosis is performed in a state where the NOx catalyst is not present, so the influence of NOx catalyst in the abnormality diagnosis can be removed, and abnormalities in the NOX sensor after the catalyst can be detected appropriately, with high diagnostic accuracy. Can be secured. Even if the NOx sensor after the catalyst detects an abnormal value, there is no confusion about whether the NOx catalyst is abnormal or the post-catalyst NO X sensor is abnormal. Can be detected.

According to a second aspect of the present invention, in the first aspect,

Catalyst temperature acquisition means for detecting or estimating the temperature of the NO X catalyst is provided, and the abnormality determination means is the catalyst temperature force detected or estimated by the catalyst temperature acquisition means. The temperature should not substantially occlude NO X The NOx concentration detected by the post-catalyst NOX sensor is compared with the NOx concentration detected or estimated by the pre-catalyst NOX concentration acquisition means under the above conditions, and the post-catalyst NOX sensor Judging abnormalities

It is characterized by that.

If the temperature of the N O X catalyst is not within a predetermined temperature range, N O X can be substantially not absorbed and released. Therefore, when the catalyst temperature is higher or lower than that temperature range, N O X cannot be stored. In the second embodiment, the post-catalyst N O X concentration detected when the catalyst temperature is not in such a temperature range is compared with the pre-catalyst N O X concentration to determine the abnormality of the post-catalyst N O X sensor. As a result, the N O X upstream of the N O X catalyst is passed through the N O X catalyst to reach the N O X catalyst downstream, so that the abnormality diagnosis of the post-catalyst N O X sensor can be suitably executed as in the first embodiment.

According to a third aspect of the present invention, in the first aspect,

An air-fuel ratio acquisition means for detecting or estimating the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is provided;

The abnormality determination means includes the NOX concentration detected by the post-catalyst NOX sensor under the condition that the air-fuel ratio detected or estimated by the air-fuel ratio acquisition means is the stoichiometric air-fuel ratio or a richer than that, and the catalyst Comparing with the NOX concentration detected or estimated by the pre-NOX concentration acquisition means, the abnormality of the post-catalyst NOX sensor is judged.

Even when the air-fuel ratio of the exhaust gas flowing into the NOX catalyst is the stoichiometric air-fuel ratio or higher, the NOX catalyst releases NOX and cannot store NOX. After N〇 X sensor abnormality diagnosis can be executed.

According to a fourth aspect of the present invention, in any one of the first to third aspects, there is provided a rich spike control means for executing a rich spike control for releasing NOx stored in the NOx catalyst.

The rich spike control means executes the rich spike control before detecting the NOx concentration by the post-catalyst NOX sensor. It is characterized by that.

As a result, the NOx stored in the NOx catalyst can be released in advance before the subsequent NOx concentration detection, and the influence of the stored NOx during the subsequent NOx concentration detection can be eliminated.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the pre-catalyst NOx concentration acquisition unit is configured to control exhaust gas discharged from the internal combustion engine based on an operating state of the internal combustion engine. It consists of at least one of an estimation means for estimating the NOx concentration and a pre-catalyst NOX sensor for detecting the NOx concentration of the exhaust gas upstream of the NOx catalyst.

It is characterized by that.

According to a sixth aspect of the present invention, in the fifth aspect,

The pre-catalyst N0 X concentration acquisition means comprises both the estimation means and the pre-catalyst NO X sensor,

The abnormality determination means compares the detected value of NOx concentration by the post-catalyst NOx sensor, the detected value of NOx concentration by the pre-catalyst NOX sensor, and the estimated value of NOX concentration by the estimation means, and compares the post-catalyst NOx sensor and Judgment is made by distinguishing the abnormality of the NOx sensor before the catalyst.

It is characterized by that.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the abnormality determination unit is configured to perform the post-catalyst NOX sensor under the condition that the post-catalyst NOX sensor is in an active state. Based on the detected NOX concentration, the post-catalyst N0 X sensor is judged abnormal

It is characterized by that.

According to the present invention, an excellent effect that an abnormality of the NOX sensor provided on the downstream side of the NOx storage reduction catalyst can be suitably detected is exhibited. Brief Description of Drawings

FIG. 1 is a schematic system diagram of an internal combustion engine according to an embodiment of the present invention. FIG. 2 is a time chart showing the contents of the abnormality diagnosis of one embodiment.

FIG. 3 is a flowchart showing the contents of the abnormality diagnosis process of the embodiment.

FIG. 4 is a schematic system diagram of an internal combustion engine according to another embodiment of the present invention. FIG. 5 is a flowchart showing the contents of the abnormality diagnosis process of another embodiment. BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic system diagram of an internal combustion engine according to an embodiment of the present invention. As shown in the figure, the internal combustion engine 1 burns a fuel / air mixture in a combustion chamber 3 formed in a cylinder block 2 and reciprocates a piston 4 in the combustion chamber 3. To generate power. The internal combustion engine 1 is a vehicular multi-cylinder engine (only one cylinder is shown), and is a spark ignition internal combustion engine, more specifically, a gasoline engine. However, the internal combustion engine to which the present invention is applied is not limited to a spark ignition type internal combustion engine, and may be, for example, a compression ignition type internal combustion engine, that is, a diesel engine.

In the cylinder head of the internal combustion engine 1, an intake valve V i that opens and closes an intake port and an exhaust valve V e that opens and closes an exhaust port are provided for each cylinder. Each intake valve V i and each exhaust valve V e are opened and closed by a camshaft (not shown). An ignition brag 7 for igniting the air-fuel mixture in the combustion chamber 3 is attached to the top of the cylinder head for each cylinder. Further, an indicator (fuel injection valve) 1 2 is disposed in the cylinder head for each cylinder so that fuel is directly injected into the combustion chamber 3. The bin 4 is configured as a so-called deep dish top surface type, and a concave portion 4a is formed on the top surface thereof. In the internal combustion engine 1, fuel is directly injected from the injector 12 2 toward the concave portion 4 a of the biston 4 with air being sucked into the combustion chamber 3. As a result, a mixture layer of fuel and air is formed (stratified) in the vicinity of the ignition brag 7 in a state separated from the surrounding air layer, and stable stratified combustion is executed. The intake port of each cylinder is connected to a surge tank 8 which is an intake air collecting chamber through a branch pipe for each cylinder. An intake pipe 13 that forms an intake manifold is connected to the upstream side of the surge tank 8, and an air cleaner 9 is provided at the upstream end of the intake pipe 13. An air flow meter 5 for detecting the intake air amount and an electronically controlled throttle valve 10 are incorporated in the intake pipe 13 in order from the upstream side. An intake passage is formed by the intake port, the surge tank 8 and the intake pipe 13.

On the other hand, the exhaust port of each cylinder is connected to an exhaust pipe 6 forming an exhaust collecting passage through a branch pipe for each cylinder. These exhaust ports, branch pipes and exhaust pipe 6 form an exhaust passage. The exhaust pipe 6 is provided with a three-way catalyst 11 that can simultaneously purify C〇, HC, and NOx in the exhaust gas at the upstream side, and NOx in the exhaust gas is purified at the downstream side. A possible NOx catalyst 16 is provided. In this embodiment, a CCL catalyst unit (CCL: Catalytic Converter Lean) in which the three-way catalyst 1 1 and the NO X catalyst 16 are accommodated in the same casing is used. The catalyst 11 and NOx catalyst 16 can be placed separately in separate casings. The three-way catalyst 1 1 is not absolutely necessary and can be omitted. For example, in the case of a diesel engine, there are many cases where a ternary catalyst is not provided.

An air-fuel ratio sensor 17 for detecting the air-fuel ratio (AZF) of the exhaust gas is installed upstream of the three-way catalyst 11. Further, a NOx sensor for detecting the NOx concentration of the exhaust gas, that is, a post-catalyst NOx sensor 18 is installed downstream of the N0x catalyst 16. The air-fuel ratio sensor 17 is a so-called wide-area air-fuel ratio sensor, can continuously detect an air-fuel ratio over a relatively wide area, and outputs a current signal proportional to the air-fuel ratio. However not limited thereto, the air-fuel ratio sensor 1 7 may consist called 0 ₂ sensor you sudden change output voltage stoichiometric air-fuel ratio (stoichiometric) the boundary.

The spark plug 7, the throttle valve 10, the injector 12 and the like described above are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20 as a control means. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, and a storage device, all not shown. Also, the ECU 20 has the above-mentioned as shown in the figure. Airflow meter 5, Air-fuel ratio sensor 17, Post-catalyst NOx sensor 18 power, Crank angle sensor 14 to detect the crank angle of internal combustion engine 1, accelerator opening sensor 15 to detect accelerator opening, NO X catalyst 1 Exhaust temperature sensors installed upstream and downstream of 6 (i.e., pre-catalyst exhaust temperature sensor 21 and post-catalyst exhaust temperature sensor 22 and other various sensors are electrically connected via an AZD converter (not shown), etc. Yes. The ECU 20 controls the ignition plug 7, the throttle valve 10, the injector 12, etc. so that a desired output can be obtained based on the detection values of various sensors, etc., and the ignition timing, fuel injection amount, fuel injection timing, Control the throttle opening. The pre-catalyst exhaust temperature sensor 21 is installed at a position between the ternary catalyst 11 and the NOx catalyst 16. The post-catalyst NOx sensor 18 is equipped with a heater, and the ECU 20 executes temperature control (heater control) of the post-catalyst NOx sensor 18. The output of the crank angle sensor 14 is also used to detect the engine speed Ne.

The three-way catalyst 11 simultaneously purifies CO, HC and NOx when the air-fuel ratio of the exhaust gas flowing into the catalyst is close to the stoichiometric air-fuel ratio (for example, AZF = 14.6). The air-fuel ratio range (window) that can simultaneously purify these three with high efficiency is relatively narrow. Therefore, in order for the three-way catalyst 11 to function effectively, as one aspect of the air-fuel ratio control, the air-fuel ratio of the air-fuel mixture is set so that the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 11 is close to the theoretical air-fuel ratio. Be controlled. This is referred to as stoichiometric control, and the engine operation mode when stoichiometric control is being executed is called stoichiometric operation. In this stoichiometric control, the target air-fuel ratio is set equal to the stoichiometric air-fuel ratio, so that the fuel injection amount injected from the indicator 12 and thus the air-fuel ratio detected by the air-fuel ratio sensor 17 becomes equal to the target air-fuel ratio. The air-fuel ratio is feedback controlled.

On the other hand, as another aspect of air-fuel ratio control from the viewpoint of reducing fuel consumption, the target air-fuel ratio may be set higher than the stoichiometric air-fuel ratio, that is, a lean value. This is called lean burn control, and the operation mode of the engine when lean burn control is executed is called lean burn operation. During lean burn control, as with stoichiometric control, the fuel injection amount is adjusted so that the air-fuel ratio detected by the air-fuel ratio sensor 17 becomes equal to the target air-fuel ratio. Thus, the air-fuel ratio is feedback controlled. During lean burn control, the air-fuel ratio of exhaust gas exhausted from the engine may be set to a lean value that makes NO X purification with the three-way catalyst 11 virtually impossible. In this case, a NO X catalyst 16 is provided on the downstream side of the three-way catalyst 11 1 in order to purify the NO X that has passed through the three-way catalyst 11.

The NO X catalyst 16 uses an NOX storage reduction (NSR) catalyst. The NOx storage reduction catalyst, the alumina A 1 ₂ 0 oxide such as ₃ or Ranaru substrate surface, a noble metal such as platinum P t as a catalyst component, and a NOx absorbing component is composed is carried Yes. NOx absorption components include, for example, potassium K, sodium Na, lithium Li, alkali metals such as cesium C s, alkaline earths such as barium Ba, calcium ca, lanthanum La, yttrium Y It consists of at least one selected from rare earths such as

The NOx storage reduction catalyst 16 stores N0x in the exhaust gas in the form of nitrate when the air-fuel ratio of the exhaust gas flowing into it is leaner than the stoichiometric air-fuel ratio, and the exhaust gas that flows into the NOx catalyst 16 When the fuel ratio is the stoichiometric air-fuel ratio or higher than that, the stored NOx is released and the NOx is absorbed and released. During lean burn operation, the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and the NOx catalyst 16 absorbs N0x in the exhaust. On the other hand, if NOx catalyst 16 occludes NOx to saturation, that is, full, NOx catalyst 16 can no longer occlude NOx, so NOx catalyst 16 should release NOx occluded from NOx catalyst. Rich spike control is performed to supply exhaust gas that is at the stoichiometric air-fuel ratio or richer than that. In this rich spike control, the target air-fuel ratio is temporarily set to the stoichiometric air-fuel ratio or a value richer than that, and the air-fuel ratio and thus the air-fuel ratio of the exhaust gas is controlled to the stoichiometric air-fuel ratio or a rich value lower than that. . In this way, releasing NOx from the NOx catalyst 16 to restore the NOx storage capacity of the NOx catalyst 16 is called NOx regeneration.

There are various other methods for rich spike control. For example, there is a method of providing a reducing agent supply valve separately on the upstream side of the NOx catalyst and controlling the opening of the reducing agent supply valve to supply the reducing agent into the exhaust. Reducing agents include hydrocarbon HC and monoxide in the exhaust. Carbon or other reducing components may be used, such as hydrogen, gas such as carbon monoxide, liquid such as propane, propylene, and butane or gaseous hydrocarbons, liquid fuel such as gasoline, light oil, and kerosene. Can be used. Preferably engine fuel or gasoline is used. Alternatively, so-called post injection is possible in which fuel is injected from the injectors 12 into the combustion chamber 3 in the later stage of the expansion stroke or in the exhaust stroke, and a large amount of unburned fuel is contained in the exhaust. On the other hand, the NO X absorption and release action of the NO X catalyst 16 cannot be practically performed unless the NO X catalyst 16 is within a predetermined operating temperature range. Therefore, in the present embodiment, the temperature of the NO X catalyst 16 (catalyst bed temperature) is detected or estimated. The temperature that can be directly detected by the temperature sensor embedded in the NO x catalyst is estimated as the temperature of the Nx catalyst 16 in this embodiment. Specifically, the ECU 20 estimates the catalyst temperature based on the pre-catalyst exhaust temperature and the post-catalyst exhaust temperature detected by the pre-catalyst exhaust temperature sensor 21 and the post-catalyst exhaust temperature sensor 22, respectively. Note that the estimation method is not limited to such an example.

Next, abnormality diagnosis of the post-catalyst NO X sensor 18 will be described.

In general, the feature of the abnormality diagnosis of the post-catalyst NO X sensor 18 in this embodiment is that the NO X catalyst 16 is catalyzed by the post-catalyst NO X sensor 18 under the condition that the NO X catalyst 16 does not substantially store NO X in the exhaust gas. The NOx concentration after the catalyst is detected, and the NOx concentration before the catalyst upstream of the NOx catalyst is detected or estimated, and the NOx concentration after the catalyst and the NOx concentration before the catalyst are compared with each other to compare the NOx concentration before the catalyst with each other. It is in the point of judging 18 abnormalities.

Here, “Nx catalyst does not substantially store NO X in exhaust gas” means that the normal and undegraded NOX catalyst does not substantially store NO X in exhaust gas. In other words, it means that the NOx storage capacity is temporarily extremely lowered even though the NOx catalyst is normal and undegraded. This includes a state where the NOx storage capacity of the NOx catalyst is completely absent (zero), but is not limited to the state of none.

Under the condition that NOx catalyst 16 does not substantially store NO X in the exhaust gas, NO X catalyst 16 does not work substantially and NO X flowing into NO X catalyst 16 passes through NO X catalyst 16 To the downstream side of the NO X catalyst 16. NO X upstream of NOx catalyst 16 The x concentration, that is, the pre-catalyst N◦ X concentration, and the NO x concentration downstream of the NOX catalyst 16, that is, the post-catalyst NOX concentration, are approximately equal. Therefore, if the detected value of the post-catalyst NOX concentration deviates from the pre-catalyst NOX concentration by a certain value or more, the post-catalyst NO sensor 18 can be determined to be abnormal. If the detected value does not deviate from the pre-catalyst NO X concentration by a certain value or more, the post-catalyst NO X sensor 18 can be determined to be normal. N 〇 The abnormality diagnosis is executed in the state where the X catalyst does not work, that is, the state where the NOX catalyst is not present, so the influence of the NO X catalyst in the abnormality diagnosis can be removed, and high diagnosis accuracy should be ensured. Can do. Even if the NO X sensor after the catalyst detects an abnormal value, there is no confusion as to whether the NO X catalyst is abnormal or the post-catalyst NO X sensor is abnormal. It can be detected as an abnormality. In this embodiment, the post-catalyst NOx concentration and the pre-catalyst NOX concentration detected under the condition that the catalyst temperature as the estimated temperature is a temperature at which the NOx catalyst 16 does not substantially store NOX in the exhaust gas, Are compared, and the abnormality of the Nx sensor after the catalyst is judged. As described above, the NOx catalyst 16 cannot substantially absorb and release NO when the temperature is not within a predetermined operating temperature range, and therefore the catalyst temperature is at least one of a higher temperature and a lower temperature than the operating temperature range. When it is, NOx cannot be occluded. Therefore, in this embodiment, the post-catalyst NOX concentration detected when the catalyst temperature is at least one of a higher temperature and a lower temperature than the operating temperature range is compared with the pre-catalyst NOX concentration to determine whether the post-catalyst NOX sensor is abnormal. judge. Abnormal diagnosis of the post-catalyst NO X sensor is executed using the situation where the catalyst temperature is outside the operating temperature range. The lower limit temperature T cmin of the operating temperature range is, for example, about 300 ° C, and the upper limit temperature T cma X is, for example, about 550 ° C.

Alternatively, after the detected catalyst under the condition that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 16 (the air-fuel ratio detected by the air-fuel ratio sensor 17 in this embodiment) is the stoichiometric air-fuel ratio or richer than that. By comparing the NOx concentration with the pre-catalyst NOx concentration, the post-catalyst NOX sensor abnormality may be judged. Even when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is the theoretical air-fuel ratio or higher, the NOx catalyst 16 releases NOx and cannot store NO X. NO X sensor abnormality after catalyst Diagnosis can be performed.

Further alternatively, under the condition that NOx is stored in the NOx catalyst 16 until it is saturated (full), the detected post-catalyst N0x concentration is compared with the pre-catalyst N0x concentration. An abnormality of the NOx sensor after the catalyst may be determined. Even at this time, the NOx catalyst 16 cannot occlude NOx, so this situation can be used to diagnose the abnormality of the NOx sensor after the catalyst.

On the other hand, the pre-catalyst NOx concentration is preferably the NOx concentration of exhaust gas discharged from the combustion chamber 13 of the engine 10 and estimated based on the operating state of the engine 10 (hereinafter referred to as pre-catalyst estimation). NOx concentration) and NOx concentration detected by the NOx sensor upstream of the NOx catalyst 16 (ie, NOx sensor before catalyst (see symbol 30 in FIG. 4)). Concentration), at least one of the following.

In the present embodiment, the former estimated pre-catalyst N O X concentration is used as the pre-catalyst N O X concentration. The ECU 20 calculates the pre-catalyst estimated NOx concentration according to a map prepared in advance based on the detected value of the parameter representing the engine operating state. As such parameters, for example, at least one of the engine speed Ne, the intake air amount Ga, the air-fuel ratio A / F, the exhaust temperature Teg, and the fuel injection amount Q can be used. Preferably, based on the load factor (2 G a, N e) obtained from the engine speed N e and the intake air amount G a and the air-fuel ratio AZF detected by the air-fuel ratio sensor 17, a predetermined map or the like Calculate the pre-catalyst estimated NOx concentration.

Note that when the latter pre-catalyst detection N0x concentration is used as the pre-catalyst NOx concentration, the actual detection value is used, so the data in the NOX concentration estimation map becomes inappropriate over time. Estimation error can be eliminated. If both the former and the latter are used, there is a possibility that the accuracy of diagnosis can be improved because of comparison with two values.

Since the post-catalyst NOx sensor 18 normal 'abnormality is judged based on the pre-catalyst NOx concentration, the pre-catalyst NOx concentration needs to be an accurate value. Other parts of the engine (injectors, etc.) are also diagnosed abnormally by ECU 20, and other parts If no abnormalities are detected, the pre-catalyst estimated NOx concentration can be regarded as an accurate value. This guarantees the accuracy of the estimated NOx concentration before the catalyst, and thus the reliability of the abnormality diagnosis result of the post-catalyst NO sensor 18.

In this embodiment, there is a three-way catalyst 11 on the upstream side of the NO X catalyst 16, but as will be described later, the engine is lean burned when the abnormality of the post-catalyst NOx sensor 18 is diagnosed, and the three-way catalyst 1 1 reduces NOx. The exhaust air / fuel ratio is increased to such an extent that it cannot be purified. Therefore, the influence of the three-way catalyst 1 1 is eliminated, and the three-way catalyst 1 1 can be regarded as if there is no one. Under the condition that the NOx catalyst 16 does not substantially store NOx, it is assumed that the NOx exhausted from the engine reaches the NOx sensor 18 after the catalyst after the three-way catalyst 1 1 and NOx catalyst 1 6 are treated as it is. be able to.

Next, an outline of the abnormality diagnosis of the post-catalyst NOx sensor 18 will be described with reference to FIG. Figure 2 shows the change in each value after the engine starts. (A) is the catalyst temperature T c estimated by ECU20, (B) is the post-catalyst NOx sensor 18 temperature T s (hereinafter also simply referred to as sensor temperature), and (C) is the output of the air-fuel ratio sensor 17 (Converted value to air-fuel ratio AZF), (D) shows the output of NOx sensor 18 after catalyst (converted value to NOx concentration Cr). Time t 0 is the engine start completion time. The temperature T s of the post-catalyst NO X sensor 18 is detected and controlled by the ECU 20. More specifically, the element impedance of the post-catalyst N0 X sensor 18 is detected by the ECU 20, and the post-catalyst NOx sensor 18 has a high impedance so that this element impedance becomes a predetermined value corresponding to the sensor activation. Data is controlled.

As shown in (A) and (B), when the engine is started, the catalyst temperature Tc and the sensor temperature Ts gradually rise, and eventually the catalyst temperature Tc exceeds the lower limit temperature Tcmin. The sensor temperature T s exceeds the lower limit temperature T smin (for example, about 750 ° C) and enters the active temperature range (time t 2). The sensor temperature T s is then maintained at a value slightly higher than the lower limit temperature T s m i n.

As shown in (C), the air-fuel ratio control is shifted from the stoichiometric control to the lean burn control around these times t1 and t2, and the air-fuel ratio is higher than the stoichiometric air-fuel ratio (stoky). The value is maintained (for example, about 16-18).

The air-fuel ratio at this time is such a high air-fuel ratio that NO X cannot be purified by the three-way catalyst 11. Therefore, the NO X exhausted from the engine passes through the three-way catalyst 11, but is trapped and occluded by the NOx catalyst 16 at the subsequent stage. Therefore, as shown in (D), NOx is not discharged downstream of the NOx catalyst 16.

On the other hand, if the lean burn operation is continued, the NOx occlusion amount in the NOx catalyst 16 increases. Therefore, in order to discharge this occluded NOx and regenerate the NOx catalyst 16, the rich spike control is executed as indicated by symbol a in (C). Specifically, the air-fuel ratio of the air-fuel mixture and the exhaust gas is controlled to a rich value lower than the stoichiometric air-fuel ratio. As a result, NOx stored in the NOx catalyst 16 is released, and NOx is detected on the downstream side of the NOx catalyst 16 as indicated by the symbol b in (D). In the example shown in the figure, a force before the NOx is detected by the post-catalyst NOx sensor 18, that is, before the NOx occlusion amount of the N0x catalyst 16 is full is applied. You can perform a rich spike after Ox is detected, that is, after the NOx storage capacity of the NOx catalyst 16 is full.

In the illustrated example, the catalyst temperature Tc gradually increases thereafter, and the catalyst temperature Tc exceeds the upper limit temperature Tcmax and deviates from the operating temperature range (time t3). In this embodiment, abnormality diagnosis of the post-catalyst NOx sensor 18 is performed using this timing.

First, when the catalyst temperature T c exceeds the upper limit temperature T cm a X, the rich spike control is immediately executed as indicated by the symbol c in (C). This is because NO X stored in the NOx catalyst 16 is released in advance before the subsequent NO X concentration detection, and the influence of the stored NO X in the subsequent NO X concentration detection is eliminated. In other words, it is rich spike control for pretreatment.

If a predetermined condition for the end of the rich spike is satisfied during the rich spike control (for example, if a NOx concentration peak is detected by the post-catalyst NOx sensor 18), it is considered that all the stored NOx has been released, and the rich spike control is terminated. (C) Shifts to lean burn control as indicated by symbol d. Then, the catalyst temperature T c becomes the upper limit temperature T cma X NOx catalyst 1 6 is also unable to occlude NO X, and NO x exhausted from the engine passes through the three-way catalyst 1 1 and NO x catalyst 1 6 and passes through the NOx sensor 1 8 To reach.

If the post-catalyst NOx sensor 1 8 is normal, the NOx concentration C r detected by the post-catalyst NOx sensor 1 8 at this time is approximately equal to the pre-catalyst estimated NO X concentration C e estimated based on the engine operating condition. It is. Therefore, after the end of the rich spike, the post-catalyst NOx concentration C r detected by the post-catalyst NOx sensor 18 at the predetermined time (time ij t 4) where the post-catalyst NOx concentration C r is stable, for example. Acquire the pre-catalyst estimated NOx concentration Ce during the same period. These NOx concentrations are compared with each other. If the post-catalyst NOx concentration C r falls within a predetermined concentration range Δ (see (D)) based on the pre-catalyst estimated NOx concentration C e, the post-catalyst NOx sensor 1 Judge 8 as normal. On the contrary, if the post-catalyst N Ox concentration Cr is outside the predetermined concentration range Δ, the post-catalyst NO X sensor 18 is determined to be abnormal. The illustrated example is an example in the case of being determined to be normal.

In the illustrated example, thereafter, the catalyst temperature Tc gradually decreases, reaches the upper limit temperature T cma X at the time t5, and enters the operating temperature range. The post-catalyst NOx concentration C r and the pre-catalyst estimated NOx concentration C e are acquired at any time from the end of the rich spike until the catalyst temperature T c falls below the upper limit temperature T cma X (t 5). .

The example described here is an example in which abnormality diagnosis is performed when the catalyst temperature Tc is higher than the operating temperature range. Instead of or in addition to this, the catalyst temperature Tc is within the operating temperature range. An example in which abnormality diagnosis is performed at a lower temperature is also possible. However, in this case, it is necessary that at least the element temperature of the post-catalyst NO X sensor 18 is in the active temperature range and the post-catalyst NO X sensor 18 is in the active state. '

Next, a specific process for executing the abnormality diagnosis as described here will be described with reference to FIG. The illustrated process is executed by the ECU 20. As a precondition for the processing here, it is assumed that lean burn control is performed so that the three-way catalyst 11 becomes incapable of NOx purification except during the rich spike control.

In the first step S 1 0 1, whether the estimated catalyst temperature T c is within the operating temperature range described above. It is determined whether the estimated catalyst temperature T c is equal to or higher than the lower limit temperature T cmin and lower than the upper limit temperature T cma χ.

When the catalyst temperature Tc is within the operating temperature range, this process is terminated. In this case, the catalyst temperature Tc may be controlled so that the catalyst temperature Tc deviates from the operating temperature range. For example, if the air-fuel ratio is changed to the rich side, the catalyst temperature Tc increases, and if the air-fuel ratio is changed to the lean side, the catalyst temperature Tc decreases.

On the other hand, if the catalyst temperature Tc is not in the operating temperature range, whether or not the post-catalyst Ν Ο χ sensor 18 is active in step S 1 0 2, that is, the post-catalyst NOX sensor 18 temperature T s is the active temperature It is determined whether the temperature is higher than the lower limit temperature T smin.

If the post-catalyst N O X sensor 18 is not in the active state, this process is terminated. If the post-catalyst N O X sensor 18 is in the active state, the rich spike control is executed in step S 1 0 3.

Thereafter, in step S 104, it is determined whether or not the rich spike control has been completed, that is, whether or not a predetermined rich spike termination condition has been established. When the rich spike control is not completed, that is, when it is being executed, this processing is terminated, and when the rich spike control is completed, the process proceeds to step S 1 0 5. Note that a step waiting for the elapse of a predetermined time may be added between step S 1 0 4 and step S 1 0 5.

In step S 1 0 5, the value of the pre-catalyst estimated N O X concentration Ce that is estimated based on the engine operating state is acquired. Next, at step S 1 0 6, the value of the post-catalyst N O X concentration C r detected by the post-catalyst N O X sensor 18 is acquired.

Next, in step S 107, the post-catalyst N O X concentration C r and the pre-catalyst estimated N O x concentration C e are compared to determine whether or not these concentrations are substantially equal to each other. Specifically, the difference between the post-catalyst NOX concentration C r and the pre-catalyst estimated NOX concentration C e, that is, the concentration difference AC is calculated by the formula: AC = IC r−C e | It is determined whether the value AC s is greater.

When the concentration difference ΔC is equal to or less than the predetermined value ΔC s, the post-catalyst NOX concentration C r is regarded as substantially equal to the pre-catalyst estimated NOX concentration C e, and the post-catalyst NOX sensor 1 8 in step S 1 0 8 Is determined to be normal. On the other hand, if the concentration difference AC is greater than the predetermined value AC s, the post-catalyst N Ox concentration C r is considered to be relatively deviated from the pre-catalyst estimated N0x concentration C e, and in step S 109 the post-catalyst NO X sensor 18 is determined to be abnormal. This process is completed.

As described above, the NO X concentration C r after the catalyst and the estimated NO X concentration C e before the catalyst are obtained under the conditions where the NO X catalyst 16 cannot substantially store NO X (under temperature conditions). Therefore, the abnormality of the post-catalyst NO X sensor 18 is judged, so that the abnormality diagnosis can be performed without being affected by the intervening NO X catalyst 16. Therefore, suitable for high diagnostic accuracy

7

Abnormal diagnosis can be realized. In addition, there is no need to add a specific part such as adding a NO X sensor at the same position, which is advantageous in terms of cost and does not require complicated control. Of course, it is also suitable for on-board diagnosis.

Next, another embodiment of the present invention will be described. Since this another embodiment is substantially the same as the previous embodiment, the following description will focus on the differences.

As shown in FIG. 4, in the internal combustion engine 1 of the present embodiment, a pre-catalyst NO X sensor 30 is additionally provided in the exhaust passage on the upstream side of the NOx catalyst 16. The pre-catalyst NOx sensor 30 detects the NOx concentration upstream of the NOx catalyst (pre-catalyst detected NOx concentration). In the illustrated example, the pre-catalyst NO X sensor 30 is arranged upstream of the three-way catalyst 11. However, the present invention is not limited to this example. For example, the pre-catalyst NOx sensor 30 is connected to the three-way catalyst 11 and N. 〇 You can place it between x catalyst 1 6.

Generally, in this alternative embodiment, the pre-catalyst NOx concentration detected by the post-catalyst NOx sensor 18, the pre-catalyst detected NOx concentration detected by the pre-catalyst NOx sensor 30, and the pre-catalyst estimate estimated based on the engine operating condition Comparison of NOx concentration is performed. Based on the comparison result, the abnormalities of the post-catalyst NOx sensor 18 and the pre-catalyst NOx sensor 30 are distinguished and determined.

More specifically, based on the estimated pre-catalyst NOx concentration, first, the detected pre-catalyst NOx concentration is compared with the pre-catalyst estimated NOx concentration. Pre-catalyst NOX sensor 30 is not affected by the three-way catalyst 1 1 and NOx catalyst 16 and directly detects NOx emitted from the engine Therefore, if the pre-catalyst detected NO x concentration deviates significantly from the pre-catalyst estimated NO x concentration, the pre-catalyst NO x sensor 30 can be determined to be abnormal. In this way, the abnormality of the pre-catalyst NO X sensor 30 can also be detected, so that the range of abnormality diagnosis can be expanded.

Next, when the before-catalyst NO X sensor 30 is determined to be normal, the after-catalyst NO X concentration is compared with the before-catalyst detected NO X concentration. Under conditions where the three-way catalyst 11 and the NOx catalyst 16 cannot purify and store NOx, the post-catalyst NOx concentration and the pre-catalyst detected NOx concentration should be approximately equal to each other. Therefore, if the post-catalyst NOx concentration deviates significantly from the pre-catalyst detected NOx concentration, the post-catalyst NOx sensor 18 can be determined to be abnormal. For comparison at this time, the post-catalyst N O X concentration may be compared with the pre-catalyst estimated N O X concentration.

FIG. 5 shows specific processing according to this other embodiment. As described above, the process shown in the figure is executed by the ECU 20, and it is assumed that the lean burn control is performed so that the three-way catalyst 11 cannot be NOx purified except during the rich spike control. .

Steps S 20 1 to S 206 are the same as Steps S 1 0 1 to S 1 06 described above. In step S 207, the value of the pre-catalyst detected NO X concentration C f detected by the pre-catalyst NOx sensor 30 is acquired.

Thereafter, in step S208, the pre-catalyst detected NOx concentration C f is compared with the pre-catalyst estimated NOx concentration Ce to determine whether or not these concentrations are substantially equal to each other. Specifically, the difference between the pre-catalyst detected NOx concentration C f and the pre-catalyst estimated NOx concentration C e, that is, the first concentration difference Δ. 1 force Formula: AC l = | C f — C e | It is determined whether this first concentration difference Δ〇 1 is greater than a first predetermined value Δ〇 1 s.

If the first concentration difference △ ○ 1 is larger than the first predetermined value △ ○ 1 s, it is considered that the pre-catalyst detected NOx concentration C f is relatively deviated from the pre-catalyst estimated NO X concentration Ce, and step S 20 9 determines that the pre-catalyst NOx sensor 30 is abnormal. On the other hand, if the first concentration difference ΔC 1 is equal to or less than the first predetermined value ΔC 1 s, the pre-catalyst detected NO X concentration C f is regarded as substantially equal to the pre-catalyst estimated NOx concentration Ce, and step S 2 1 Go to 0. In step S210, the after-catalyst NO x concentration C r and the before-catalyst detected NO x concentration C f are compared, and it is determined whether or not these concentrations are substantially equal to each other. Specifically, the difference between the post-catalyst NO X concentration C r and the pre-catalyst detected NO X concentration C f, that is, the second concentration difference Δ C 2 force formula: AC 2 = | Cr − C f | It is then determined whether or not the second concentration difference AC2 is greater than a second predetermined value AC2s.

If the second concentration difference AC2 is greater than the second predetermined value Δ〇2 s, the post-catalyst Ν Ο χ concentration C r is considered to be relatively deviated from the pre-catalyst detected NO X concentration C f, and step S 21 At 1, the post-catalyst NO X sensor 18 is determined to be abnormal. On the other hand, if the second concentration difference AC 2 is equal to or less than the second predetermined value AC 2 s, the post-catalyst NO x concentration Cr is regarded as substantially equal to the pre-catalyst detected NO x concentration C f, and the process proceeds to step S212.

In step S 21 2, it is determined that both the before-catalyst NO X sensor 30 and the after-catalyst NO X sensor 18 are normal. This process is completed as described above.

As mentioned above, although embodiment of this invention was described, this invention can also take other embodiment. For example, in the above embodiment, when comparing NOx concentrations, the comparison is made based on these differences. However, the present invention is not limited to this. For example, the comparison may be performed based on these ratios. The pre-treatment rich spike control (steps S 103 and S 203) is performed immediately after the catalyst temperature T c deviates from the operating temperature range as in the above embodiment, and immediately before the catalyst temperature T c deviates from the operating temperature range. It is also possible to do this. It is also possible to omit the pre-processing latch spike control. It is also possible to carry out a control that fluctuates the NOx concentration of the exhaust gas forcibly and compares the NOx concentrations detected at this time to determine the abnormality.

The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention. Industrial applicability

The present invention is applicable to an N O X sensor provided in an exhaust system of an internal combustion engine.

Claims

The scope of the claims

1. an NOx storage reduction catalyst provided in an exhaust passage of an internal combustion engine;

A pre-catalyst N0x concentration acquisition means for detecting or estimating the NOx concentration of exhaust gas upstream of the NOx catalyst;

The NOX concentration detected by the post-catalyst NOX sensor and the NO X concentration detected or estimated by the pre-catalyst NOX concentration acquisition means under the condition that the NO X catalyst does not substantially store NO X in the exhaust gas. And an abnormality determination means for determining abnormality of the post-catalyst NO X sensor

An N O X sensor abnormality diagnosis device characterized by comprising:

2. A catalyst temperature acquisition means for detecting or estimating the temperature of the NO X catalyst is provided, and the abnormality determination means is configured such that the catalyst temperature detected or estimated by the catalyst temperature acquisition means is exhausted by the NOX catalyst. The NO X concentration detected by the post-catalyst NO X sensor and the NO detected or estimated by the pre-catalyst NO X concentration acquisition means under the condition that the NO X in the gas is not substantially occluded. Compare the X concentration to determine the NO X sensor abnormality after the catalyst

The apparatus for diagnosing abnormality of an N O X sensor according to claim 1.

3. Air-fuel ratio acquisition means for detecting or estimating the air-fuel ratio of the exhaust gas flowing into the NO X catalyst is provided,

The abnormality determination means includes the NOX concentration detected by the post-catalyst NOx sensor under the condition that the air-fuel ratio detected or estimated by the air-fuel ratio acquisition means is the stoichiometric air-fuel ratio or a richer than that, and the catalyst Compare the NOx concentration detected or estimated by the pre-NOX concentration acquisition means to determine the abnormality of the post-catalyst NOx sensor The abnormality diagnosis device for a NO X sensor according to claim 1, wherein

4. Rich spike control means for performing rich spike control for releasing NO X stored in the NO X catalyst is provided,

The rich spike control means executes the rich spike control before detecting the NO X concentration by the post-catalyst NO X sensor.

4. The abnormality diagnosis apparatus for an N0 X sensor according to claim 1, wherein

5. The pre-catalyst NO X concentration acquisition means includes estimation means for estimating the NO X concentration of exhaust gas discharged from the internal combustion engine based on the operating state of the internal combustion engine, and exhaust gas upstream of the NO X catalyst. Consists of at least one pre-catalyst NOX sensor that detects gas NOX concentration

The apparatus for diagnosing abnormality of a NO X sensor according to any one of claims 1 to 4.

6. The pre-catalyst NO X concentration acquisition means comprises both the estimation means and the pre-catalyst NO X sensor,

The abnormality determination means compares the detected value of NO X concentration by the post-catalyst NO X sensor, the detected value of NO x concentration by the pre-catalyst NO X sensor, and the estimated value of NO X concentration by the estimation means. Judgment is made by distinguishing the abnormality of the post-catalyst NOX sensor and the pre-catalyst NOX sensor.

6. The abnormality diagnosis apparatus for an N O X sensor according to claim 5.

7. The abnormality determination means determines an abnormality of the post-catalyst NOX sensor based on a NOX concentration detected by the post-catalyst NOX sensor under a condition that the post-catalyst NO X sensor is in an active state. The apparatus for diagnosing abnormality of a NO x sensor according to any one of claims 1 to 6.